The present invention relates to mobile vehicles. More particularly, the invention relates to on-highway vehicles designed to operate at highway speeds.
Special terms used herein are defined as follows:
Forward: Toward the front end of the vehicle.
Aft: Toward the rear end of the vehicle.
Highway speeds: Speeds in excess of fifty miles per hour.
Extended motor vehicle: A motor vehicle having an elongated, integral chassis.
Elongated: Substantially longer than a conventional automobile; having a length of from about fifteen to about forty feet.
Integral: Unitary; not segmented; not formed e.g. like a tractor-trailer.
Axle: A shaft which connects wheels located on opposite sides of a frame which is supported by the shaft.
Short axle: A shaft which connects a pair of wheels on the same side of the frame.
Spindle: A short conical shaft on which a wheel is mounted.
Driving axle: Axle that is power-driven.
Fixed axle: An axle permanently aligned in a particular configuration with respect to the frame.
Steerable axle: An axle which is capable of changing orientation with respect to the frame.
Tandem axles: A pair of axles very near one another; not spaced apart or separated by a distance of more than about two or three feet.
Tridem axles: Three axles very near one another; not spaced apart or separated by a distance of more than about two or three feet.
Spread axles or spread-tandem axles: Axles spaced apart and separated by a distance of about ten feet.
Fixed wheel: A wheel the orientation of which remains unchanged with respect to an axle on which the wheel is mounted.
Steerable wheel: A wheel which is capable of changing direction with respect to and independently of a fixed axle to which the wheel is connected by a spindle.
Much of the background information relating to the present invention may be found in U.S. Pat. Nos. 4,740,006, 5,026,085, 5,071,152, 5,123,669, 5,135,064, 5,139,103, and 5,232,238 to Ducote, and in application Ser. No. 807,199 by Ducote. Said patents and application are hereby incorporated by reference.
Mobile vehicles encompassed by the present invention include tractor-trailers, recreation-vehicle (RV) motor homes, boat-trailer assemblies, trucks, busses, moving vans, passenger vans, and fire engines.
Trucks, tractors, and trailers are well described in the Encyclopedia Britannica, volume 18, pages 721-723, hereby incorporated by reference.
Axles with forcibly-steered wheels are disposed at the front ends of automotive vehicles. The wheels are manually steered by a driver by means of a steering wheel. The axles are designed to have a single wheel with a tire at each end of the axle. Rotary movement of the steering wheel causes the ends of the steerable spindles on which the wheels are mounted to move forward or rearward. The wheels mounted on the spindles change lateral alignment with the vehicle. This causes the vehicle to steer to the right or to the left.
In 1984 the U.S. Department of Transportation published the Bridge Gross Weight Formula EQU W=500[LN/(N-1)+12N+36]
in which
W=the maximum weight in pounds that can be carried on a group of two or more axles to the nearest 500 pounds PA1 L=spacing in feet between the outer axles of any two or more consecutive axles and PA1 N=number of axles being considered
This formula pertains to eighteen-wheelers and single-unit trucks using the interstate highway system.
The Bridge Gross Weight Formula provides a standard to regulate the spacing of trailer and truck axles, and the maximum weight that single axles and axle groups are permitted on interstate highways. The weight limits for the interstate highway system are twenty thousand pounds per single axle, thirty-four thousand pounds per tandem axles, and eighty thousand pounds total gross weight.
Marine intermodal containers were introduced in 1963. The length of an intermodal container was originally twenty or forty feet. This is an efficient way to move freight. Container-handling equipment moves a twenty or forty-foot box. This, in lieu of stevedores' moving sacks or crates. This efficient concept has been introduced into shipping by steamships, trucks, and railways. There is no legal limit to the weight which steamship and railroads can carry. The gross weight that eighteen-wheelers can carry via intermodal containers is limited to eighty thousand pounds.
In 1983 the trailer moiety of tractor-trailers was forty-two feet in length. Trailers being built today--1993--are between forty-eight and fifty-three feet in length. Domestic intermodal containers are now also between forty-eight and fifty-three feet long. These containers are collected by trucks and delivered to a railhead. The "long haul" is by rail. At the end of the rail trip the domestic containers are reloaded onto trucks for delivery at their destination. The permissible gross weight of each truck is again eighty thousand pounds.
The domestic intermodal containers are double-stacked on the rail cars. First the forty-eight-foot containers are onloaded; then fifty-three-foot containers are placed on top of the forty-eight-foot containers.
Much study has been given to increasing the productivity and efficiency of our surface transportation system. Advances have been made in increasing the cubage for low-density commodities. The industry is striving for an increase in allowable truck gross weight. The allowance for the axle groups specified in the Bridge Formula are thirty-four thousand, thirty-four thousand, and twelve thousand pounds for trailer tandem, tractor tandem, and truck front axles, respectively. The sum of these allowances is eighty thousand pounds. Full parity is allowed for axle groups and for the vehicle gross weight. Increased allowance for axle groups which would increase the total allowable gross weight for the vehicle would be abusive and eventually destructive of the highways and the interstate infrasystem.
The Bridge Formula specifies an allowable weight of twenty thousand pounds per single axle. A configuration of five single axles would yield a significant increment in allowable vehicle gross weight. The individual axle allowances of twenty thousand, twenty thousand, twenty thousand, and twenty thousand pounds, plus twelve thousand pounds for the front axle, adds up to a total of ninety-two thousand pounds. An increase in allowable gross weight from eighty thousand pounds for the conventional eighteen-wheeler to even eighty-eight thousand pounds (as was "grandfathered" into the regulations after the Bridge Formula was applied) would result in a payload increase of twenty-two percent. A street or highway sustains less wear from a single axle carrying twenty thousand pounds than from a pair of tandem axles carrying thirty-four thousand pounds. The force or pressure of the weight from axle groups on the road foundation is said to be directed in the form of a triangle with the vertex pointed down at the road surface.
Roads that easily sustain traffic wear from a twenty-thousand-pound single axle may not sustain traffic wear from a pair of thirty-four-thousand-pound tandem axles. If the road foundation should rest on substandard soil, or if there is water seepage through the soil on which the road foundation rests, the foundation may eventually crumble. It is therefore a significant benefit to have a twenty-thousand-pound single axle load on a street or roadway instead of a thirty-four-thousand-pound tandem load.
The Federal Bridge Formula pertains to interstate highways. States, counties or parishes, and municipalities have jurisdiction over streets and roads within their domain which they have built and which they maintain. A city, county/parish, or state can enact legislation or regulations which provide for increased permissible gross weight for axle configurations comprising five single axles. This increase would apply to marine and domestic intermodal containers on trailers and truck chasses. The containers can be moved by trucks within a city, county, parish, or state which has increased the gross allowance. They can be moved by rail across a region that does not allow the increase in truck/trailer gross weight, to another city, country, parish, or state which does allow said increase.